1. Field of the Invention
Embodiments of the present invention relate to a semiconductor device that uses silicon or a semiconductor material having a wide bandgap, and a method of manufacturing a semiconductor device.
2. Description of the Related Art
In semiconductor devices such as power devices, an edge termination structure called a junction termination extension (JTE) and that reduces the level of charge stepwise in an outer peripheral direction from a p+ region of an outer periphery of an active region in order to establish an element breakdown voltage level is often employed (for example, refer to Published Japanese-Translation of PCT Application, Publication No. 2001-508950).
Further, a second-conductivity-type region is selectively formed in a front surface or rear surface of a semiconductor substrate of a first conductivity type and by changing the impurity concentration of this second-conductivity-type region, a semiconductor device is formed. In a JTE region, the carrier concentration is reduced stepwise on the semiconductor substrate to control the level of charge.
FIG. 4 is a cross-sectional view of a traditional JTE structure. A Schottky barrier diode will be described as an example. For example, on an n+ semiconductor substrate 1 that is a material such as silicon carbide (SiC), an n− region 2 that is a drift layer is formed by epitaxial growth. On the n− region 2, for example, an active portion p+ region 3 implanted with, for example, aluminum (Al) is formed and for example, a Schottky metal 5 such as titanium (Ti) is provided thereon.
In an outer periphery of the p+ region 3, a p region 41 having a low carrier concentration is formed and in a periphery farther outward, a p− region 42 having an even lower concentration is formed. With such a configuration, when voltage of a reverse direction is applied, electric field concentration occurring in the edge termination structure is relaxed, enabling a required breakdown voltage level to be established.
FIG. 5 is a cross-sectional view of a traditional space-modulated JTE structure. The ratio of the p− region 42 to the p region 41 varies stepwise with distribution whereby the extent of electric field concentration may be further relaxed and the breakdown voltage level may be further improved. Such an edge termination structure is a technology used not only in Schottky barrier diodes but also in MOS power devices such as metal oxide semiconductor field effect transistors (MOSFET), insulated gate bipolar transistors (IGBT), and the like.